Although epidemiological studies show that viral infection is an important associated event in Sudden Infant Syndrome (SIDS), the mechanism of the association is unclear. A consensus opinion is that viruses do not function alone in the pathogenesis of SIDS but operate to initiate or to perpetuate a chain of events leading to death. A hypothesis that would be consistent with most of the epidemiologic and pathologic findings in SIDS is that viruses may operate through IgE mediated hypersensitivity. We propose to investigate the role of hypersensitivity to viruses by measurement of virus specific IgE antibody against isolated from and detected in SIDS cases and by searhing for histologic and biochemical evidence of hypersensitivity reactions. Isolation and detection of viruses will be by a) direct isolation (CPE), b) intrinsic interference, and c) immunofluorescent antibody. Measurements will include 1) neutralizing antibody titers in serum and bronchial washings against viruses isolated, 2) total IgE protein in serum and of IgE and IgA in bronchial washings, 3) virus specific IgE in serum and of virus specific IgE and IgA in bronchial washings, 4) total histamine content of lung samples, 5) interferon in bronchial washings and cerebrospinal fluid. Study of total histologic sections of lung, bronchi, trachea, and larynx will be performed to determine if morphologic changes in the tissue mast cells are present.